AN ICHTHYOBDELLID PARASITIC ON SAND WHITING. 7 
present ; some of these show through from the dorsal surface. 
Large and more diffuse yellow cells are scattered about the 
surface, and at the posterior region of the body certain of the 
cocoon glands have a light brown colour. 
Viewed from the dorsal surface the lighter coloured pigment 
cells of the neck region are seen to be placed in a single 
lateral and a medial double row. 
The darker cells are found in a well-marked single row 
along the mediad wall of the contractile lacuna and are 
plentiful, but without any apparent regular arrangement in 
the dorsal body wall. 
The lighter cells appear as five irregular rows in each side 
of the body. 
In a living specimen the two eye-spots are very con- 
spicuous. They are of a rich dark reddish-brown colour, 
larger than any of the pigment cells and characterised by 
their regular outline in place of the fringed appearance of 
the pigment cells. In the drawing they are shown as seen 
from the ventral surface through the body tissues. 
A microscopic examination of the caudal fin of a living 
sand whiting to which a leech was attached showed a remark- 
able similarity in colour and arrangement of the pigment cells 
of the two animals. 
So far as my observations go the pigment cells lose their 
fringed character in strong light and become more regular in 
outline. 
Movements. 
During my observations of living specimens I never saw an 
individual swimming, neither could I, by dropping the leeches 
into salt water, cause any swimming motion. They would 
fall straight to the bottom of the beaker and then move 
slowly along the surface of the glass by leech-like movements. 
These observations were made on leeches ranging in size from 
2 to 12 mm. They have a bearing on the question of the 
deposition of the cocoon and the manner of infestation of 
sand whiting by young leeches. Johannson (1898), writing* 
